Keith Hackett's verdict

1) Award a penalty and show the keeper a red card for denying an obvious goalscoring opportunity (known among officials as "DOGSO"). You should also show the defender a yellow card for unsporting behaviour – it's not a red for him because he was not directly guilty of DOGSO. The game cannot restart without a goalkeeper, so make sure either a sub keeper is brought on, or an outfield player goes in goal. Thanks to Steven Miller. 2) Yes – there's no reason to stop him changing so long as he's wearing a distinguishing colour. Also check that the shirt has the same sponsor as the rest of his team, and that it conforms to any specific competition rule which might require him to wear the registered kit. Thanks to Laszlo Sandler. 3) Play on. It's unfortunate, but the ball striking the additional assistant referee is treated the same way as if the ball struck you: all officials are considered part of the field of play. But you need to make clear to your assistant once the ball is out of play that he should be more aware of his positioning. Joe Stark wins the shirt.